Horses of the Dawn, book 1: The Escape
Kathryn Lasky2012

Run Wild. Run Free.

The horses are in danger. They were rounded up by the two-legs and forced onto a boat to cross the wide ocean. The journey went badly and the boat was deemed too heavy, so the two-legs forced the horses into the sea and sailed away, leaving the herd to die in the deep.

By a miracle, the horses survived and made it to land. All but one -- the ghost horse, the leader of the pack. Now it's up to her daughter, only a filly, to take charge of the terrified herd. Stranded in a new land, surrounded by two-legs, will the horses find a way to live safe and free?